Conventionally, in design of communications systems there is a trade off between bit error rate (BER) and transmission bit rate. Higher bit rates tend to have higher BERs. A well-known limit on capacity of a communications channel is known as the Shannon Limit. In practice, where forward error correction (FEC) is used, the Shannon Limit is a theoretical boundary on channel capacity for a given modulation and code rate, where the code rate is the ratio of data bits to total bits transmitted for some amount of time, such as a second. FEC coding adds redundancy to a message by encoding such a message prior to transmission.
Error correction codes, including one or more used in FEC, classically exist as block codes (Hamming, Bose-Chaudhuri-Hochquenghem (BCH), and Reed-Solomon), convolutional codes (Viterbi), trellis codes, concatenated (Viterbi/Reed-Solomon), turbo convolutional codes (TCCs) and turbo product codes (TPCs). With respect to TPCs, an extended Hamming code (a Hamming code with a parity bit) and parity codes are commonly used to construct product codes.
Others have suggested serial concatenated TCC encoding, then interleaving output from that first TCC encoding followed by TCC encoding again the interleaved output. Others have suggested that such serial concatenated TCC encoding is not bandwidth efficient and exhibits an undesirable error floor phenomenon. However, with respect to TPCs, it should be understood that they are based on block codes and not convolutional codes.
Enhanced TPCs (eTPCs) add another dimension or error correction by encoding along diagonals of a TPC matrix, namely, after encoding rows and columns. Conventionally, encoding along the diagonals has been done with a simple parity code. So, for example, in eTPC simple parity coding is done on post-interleaved rows.
Accordingly, it would be both desirable and useful to provide FEC having more powerful encoding than conventional eTPC to improve BER.